Check your fan, original is a clutch fan. Try and spin it by hand, should only spin less than a turn or so. If it spins freely it's worn out. Double check your coolant level. Don't open the cap hot.
Your upper hose should get hard and hot when the thermostat opens, no pun intended.
Be careful around a running engine!
the fan does turn freely ! but it always did, i thought it was normal... you think that would get the engine to overheat ?
concerning the coolant level, it was full by looking at the radiator fill up hole before starting the engine. Haven't opened it since, would that be enough ? i suspect some air in the cooling system... how can I be sure if it's 100% coolant, and no air in the circuit ?